The present invention generally relates to communication networks, and more particularly to a communication network having multi-conjunction architecture.
A lattice communication network analogous to nerve cells of a living body was proposed in a U.S. Pat. No. 4,516,272 in which the assignee is the same as the assignee of the present application. According to this proposed communication network, each node apparatus has a plurality of input and output channels and is used as a communication control element, and such node apparatuses are coupled in a multi-conjunction to constitute the lattice communication network. Each node apparatus transfers one of incoming signals according to a first-come-first-served logic (hereinafter referred to as a first-come-first-output logic).
In addition, a multi-channel lattice communication network applicable to local area networks (LANs), public line networks and especially to a multi-media communication was previously proposed in a U.S. Pat. No. 4,839,887 in which the assignee is the same as the assignee of the present application. In an initial state of this previously proposed lattice communication network where no communication is made between the input and output channels of the node apparatus, signals can pass through the node apparatus because an input port and an output port thereof are coupled through a switching gate of the node apparatus. In this initial state, each input channel is coupled to all of the output channels except the output channel having a channel number corresponding thereto.
When an input signal is supplied to one of the input channels in the initial state, the first receiving input channel which receives the input signal first is detected according to the first-come-first-output logic. Hence, only the first receiving input channel is coupled to those output channels other than the output channel having a channel number corresponding to that of the first receiving input channel. In other words, a broadcast communication is made by transferring the input signal which is received by the first receiving input channel to all of the output channels except the output channel having the channel number corresponding to that of the first receiving input channel. All of the input channels other than the first receiving input channel are disconnected from the output channels. As a result, it is possible to prevent a dropout of message packets.
Each node apparatus has a function of returning an active signal when the first receiving input channel is detected, and the active signal is outputted from the output channel having the channel number corresponding to that of the first receiving input channel. A node apparatus which receives the active signal can recognize that the output channel from which the sending signal was sent has been detected as the first receiving input channel in the node apparatus which returned the active signal.
In the previously proposed lattice communication network, a source terminal device which originates a communication must wait for a link time constant corresponding to the time it takes for the active signal to be returned to each node apparatus from neighboring node apparatuses after the communication is broadcast within the entire lattice communication network. The link time constant is set greater than or equal to two times a maximum propagation delay time of a span, that is, a line between the adjacent node apparatuses. Hence, the link time constant is dependent on a maximum distance of the line between the adjacent node apparatuses within the lattice communication network. For this reason, when an extremely long line is included in a portion of the lattice communication network, the link time constant of all of the node apparatuses in the lattice communication network must be set to a large value in accordance with the extremely long line even when the traffic of the extremely long line is considerably small.
A network time constant of the lattice communication network, that is, a time in which a receipt of a first returning signal from a destination terminal device is guaranteed, is set to a sum of two times the propagation delay time of a maximum tolerable network length and a time it takes for the destination terminal device to start sending the first returning signal. Hence, the network time constant must also be set to a large value depending on the existence of the extremely long line between the adjacent node apparatuses within the lattice communication network.
Therefore, when the extremely long line between the adjacent node apparatuses exists within the lattice communication network, the link time constant and the network time constant must be set to large values and a through-put of the lattice communication network as a whole becomes poor. The through-put becomes poor even when the extremely long line occupies only a small portion of the lattice communication network, and the efficiency of the lattice communication network is especially poor in such a case.
On the other hand, an Ethernet (registered trademark) is disclosed in "Internet Transport Protocols", Xerox System Integration Standard, XSIS 028112, December 1981. When connecting a plurality of communication networks, a network address is assigned to each communication network and a repeater station called an internetwork router host is used to couple the communication networks. The internetwork router relays a communication which is broadcast extending over a plurality of communication networks. The internetwork router has a routing table which stores a delay, a directly-connected communication network on which to transmit the packet, if the delay is not zero the host number of an internetwork router on the directly-connected communication network, and a timer used in the routing table maintenance algorithm.
The internetwork router does not know the host number other than that of the internetwork router on the directly-connected communication network. For this reason, it is necessary to know beforehand the network address of the communication network which includes a destination host. In order to find out the communication network which includes the destination host, an inquiry is made to each of the communication networks by use of a high level protocol (level 3) called clearinghouse. When the communication network including the destination host is found, the communication is made by directly designating the network number and the host number. Therefore, there is a problem in that the communication requires a complex procedure. In addition, when sending a short message to a large number of destination hosts, there is a problem in that the through-put becomes extremely poor.